JP2022527484A - Microwave device and method - Google Patents

Abstract

Microwave devices and methods are provided. The microwave device is configured to deliver microwave energy with a selected operating frequency or frequency range to a radiating element extending from or coupled to the distal end of the microwave feed line. The wave feed line, the radiating element, and the reactorance element formed in or on the microwave feed line are provided, and the operating frequency or frequency range is such that the reactorance element determines the impedance of the radiating element and the impedance of the microwave feed line. It is selected to reduce or eliminate the surface current flowing to the ground of the feed line while providing the desired degree of matching between.

Description

The present invention relates to microwave antenna devices and methods, eg, microwave antenna devices in which reactance devices provide both impedance matching and reduction or elimination of surface currents.

It is known to use interstitial antennas in medical energy systems to deliver energy to living tissue for ablation or non-ablation purposes. In most energy ablation systems, energy is delivered from the energy generator to a radiant applicator that transfers the energy to the tissue via a connecting cable. In these applicators, the radiating element is either surrounded by tissue or placed in contact with tissue. In such systems, standard practice is typically to raise the temperature of the tissue from 43 ° C to 45 ° C, for example above 60 ° C, 70 ° C or 100 ° C. Delivering energy for treatment that lasts for any time of 1 to 20 minutes. The temperature of the tissue may be increased so that necrosis occurs within the desired ablation zone. The energy may be delivered to have an amplitude modulation or pulse width modulation duty cycle to ensure that the required level of energy is maintained or controlled during energy release.

One undesired aspect of treatment may be the presence of radiation from the antenna surface current. Radiation from the antenna surface current can heat or ablate adjacent healthy tissue beyond the desired target ablation zone. In some situations, additional radiation can distort the ideal isotropic (eg, spherical) necrotic zone into a more tear-shaped (teardrop) shape, which can be a problem when planning ablation. be.

Typically, the ablation antenna is formed around a monopole or dipole method that utilizes the arrangement of the inner and outer conductors of the coaxial transmission line to produce a radiating element that matches the impedance of the tissue target. Alternating current flowing through the antenna generates electromagnetic waves that are radiated to surrounding tissues. The current flowing in the antenna element connected to or coupled to the outer conductor of the transmission line returns to the generator by flowing on the outer conductor of the coaxial transmission line.

The current returned to the generator by flowing down the outer conductor of the coaxial transmission line is sometimes referred to as the common mode current. These common-mode currents can induce radiation from the outer conductors of the coaxial transmission line and distort the antenna radiation pattern. The overall electrical length of the transmission line can have a significant effect on the transmission line's sensitivity to common mode currents.

Baluns can be used to balance even and odd mode currents between the radiating element and the outer conductor of the transmission line. The balun matches the phase of the balanced radiating element to the unbalanced coaxial feed line to prevent common mode currents from flowing. By preventing the flow of common mode current, a uniform electric field pattern can be ensured.

One of the limitations of the balun is that the balun may contain a quarter wavelength portion, which may impose spatial constraints on the design. Dielectric loads are known to be used to reduce the physical size of transmission lines of the same electrical length. Dielectric loads are often used to maintain a compact shape. Commonly used dielectrics include various microwave ceramics such as alumina, zirconia or water jackets. Usually, a dipole antenna is a balanced antenna, while a monopole antenna is an unbalanced antenna. In the case of a monopole antenna, an unun may be used as opposed to a balun to match the unbalanced line to the unbalanced radiating element.

Another way to reduce surface current is to form a conductive sleeve or shield around the outer tread. The conductive sleeve or shield utilizes phase to offset unwanted surface currents to capture and reflect surface currents. The conductive sleeve or shield may be referred to as a choke or sleeve balun or bazooka balun. The choke or sleeve or bazooka balun can typically be grounded to the outer conductor to form a quarter wavelength portion and filled with a dielectric to further reduce its size.

The methods described above increase the complexity and manufacture of the antenna structure, for example by physically increasing the diameter of the antenna structure to accommodate all the components required to form a balun or choke mechanism. May have geometric requirements that can increase significantly.

In a first aspect, a microwave device is provided that extends or extends microwave energy with a selected operating frequency or frequency range from the distal end of a microwave feed line or said distal end. It comprises a microwave feed line configured to deliver to a radiating element coupled to the radiating element, said radiating element, and a reactorance element formed in or on the microwave feed line, said operating frequency or frequency range. So that the reactorance element provides the desired degree of matching between the impedance of the radiating element and the impedance of the microwave feed line and reduces or eliminates the surface current flowing through the ground of the feed line. Be selected.

The microwave feed wire may include a coaxial cable. The ground may include the outer conductor of the coaxial cable.

The reactance element may include at least one opening formed in the outer conductor. The opening may be formed by selectively removing a portion of the outer conductor.

The at least one opening may include at least one longitudinal slot.

At least one conductive strip may remain between the longitudinal slots. The at least one conductive strip may form an inductive conductor element.

The reactance element further comprises at least one conductive wire disposed across the at least one longitudinal slot.

The reactance element may include at least one capacitive ring at the distal end of the coaxial cable. The capacitive ring or each capacitive ring may include a ring of outer conductor material that remains after the formation of the at least one opening.

The at least one capacitive ring may be electrically connected to the at least one inductive conductor element.

The inductive conductor element may include at least one discontinuity along the length of the inductive conductor element. The at least one discontinuity may provide capacitance.

The at least one longitudinal slot may vary in width along the length of the slot.

The at least one longitudinal slot may have a stepped width such that different portions of the longitudinal slot have different widths.

The at least one longitudinal slot may be a single longitudinal slot.

The at least one longitudinal slot may be a pair of radially opposed longitudinal slots.

The radiating element may include a monopole antenna.

The radiating element may include an exposed distal portion of the inner conductor of the coaxial cable, the inner conductor of the coaxial cable being longer than the outer conductor of the coaxial cable.

The surface current may include a common mode current.

The microwave device may be configured to perform microwave ablation of tissue in said operating frequency or frequency range. The microwave device may be configured to perform tissue hyperthermia at said operating frequency or frequency range.

In a further aspect that may be provided independently, a microwave system is provided, the microwave system comprising a microwave generator and said microwaves to generate microwave energy having a selected operating frequency or frequency range. A controller configured to control the generator and a microwave configured to deliver the microwave energy to a radiation element extending from or coupled to the distal end of the microwave feed line. The feed line, the radiating element, and the reactors element formed in or on the microwave feed line are provided, and the operating frequency or frequency range is such that the reactors element has the impedance of the radiating element and the microwave. It is selected to provide the desired degree of matching with the impedance of the feed wire and to reduce or eliminate the surface current flowing through the ground of the feed wire.

In a further embodiment that may be provided independently, the provided method is a step of controlling the microwave generator to generate microwave energy with a selected operating frequency or frequency range, and a distance of the microwave feed line. A reaction element is formed in or on the microwave feed line in a step of delivering microwave energy by the microwave feed line to a radiation element extending from the position end or coupled to the distal end. The operating frequency or frequency range, including the step, is such that the reactorance element provides the desired degree of matching between the impedance of the radiating element and the impedance of the microwave feed line, and the ground of the feed line. It is selected to reduce or eliminate the surface current flowing through it.

In a further embodiment that may be provided independently, a method of designing a microwave device is provided in which the method selects a radiating element that extends from or is coupled to the distal end of the microwave feed line. A step of simulating operation over a certain frequency or frequency range, and a step of performing an iterative design procedure to simulate the detuning of the radiating element and the reactors formed in or on the microwave feed line. In the selected frequency or frequency range, the reactorance characteristics of the reactors include the simulated impedance of the radiation element and the simulation of the microwave feed line, including the step of selecting the reactorance characteristics of the element. The iterative design procedure is repeated until the simulated surface current flowing through the ground of the feed line is reduced or eliminated while providing the desired degree of matching to the impedance.

In a further aspect that may be provided independently, a method of manufacturing a microwave device is provided, such as forming a radiating antenna element at the step of providing a coaxial cable and at the distal end of the coaxial cable. , The step of selectively removing the distal portion of the outer conductor of the coaxial cable to expose the distal portion of the inner conductor, and selectively removing at least one additional portion of the outer conductor of the coaxial cable. The step of forming at least one opening in the outer conductor of the coaxial cable and the parameters of the at least one opening are the impedance of the radiating element when operated in a selected operating frequency or frequency range. It is selected to provide the desired degree of matching between and the impedance of the microwave feed wire and to reduce or eliminate the surface current flowing through the ground of the feed wire.

The at least one opening may include at least one longitudinal slot.

Selective removal of the at least one additional portion of the outer conductor is sawing, slicing, cutting, burning, melting, erosion, flattening, polishing, hydroforming, machining, laser cutting, etching, acid erosion. Can include at least one of.

An energy control mechanism for preventing an unbalanced current that heats the antenna surface is described.

The method includes an electromagnetic energy generating system, cabling, and an applicator used to send energy from the generating system to a receiving device, eg, a radiating applicator antenna that transfers energy to living tissue.

The energy utilizes high impedance discontinuity to use the same region to limit the return of surface current to the outer conductor of the transmission line while performing impedance conversion to match the radiating element to the transmission channel. And delivered to the radiating element.

It may provide a more compact antenna for delivering microwave energy into the tissue. A simple technique can be used to match the antenna to the feed line, which can reduce the common mode current and not overly complicate manufacturing.

Impedance transducers can be used to match the antenna to the feed line. A matching network can be constructed around tuning elements such as stubs, quarter wavelength transducers (phase and impedance) or reactance tuning functions. Inductive reactance can usually be formed by the length of the central conductor. Capacitive reactance can usually be controlled by coaxial spacing. A combination of inductive reactance and capacitive reactance can be used to change the impedance. Typical reactance matching may include T and Pi network structures. A balanced Pi arrangement with an inductive grounding element (eg, an O-pad structure) increases the advantage by placing the inductive reactance on both the signal line and the ground line, which can operate like a common mode choke.

This means that, for example, a standard antenna design can match the ideal antenna to the transmission feed in one way, and then a secondary method can be adopted to handle the common mode current. Means.

The approach described herein, which may be more efficient, is a single structure, element, feature that supports unbalanced impedance matching by utilizing the return energy from antenna mismatch to offset common mode currents. , Or to generate a method. This means that the reactance characteristics of the feed line and antenna mismatch can be adjusted simultaneously so as to intentionally and destructively cancel each other out.

The inductive signal element and the grounding element are included together with the capacitive grounding element so as to generate a combined matching choke function.

In one aspect, the microwave treatment needle comprises a microwave antenna having a radiating element and tuned to deliver microwave energy to the target tissue, including a feed line grounded reactorance characteristic, in conjunction with the reactorance characteristic. The mismatch of the radiating element is used to simultaneously match and choke the surface current normally present on the feed line.

The reactance property can be realized by an inductive conductor electrically connected across a capacitive element formed in the feed line outer conductor.

The reactance capacitance characteristic can be realized by the slots of the conductive material removed from the outer conductor.

This reactance capacitance characteristic can be further realized by a conductive ring or collar on the outer conductor of the antenna.

The reactance inductive property can be realized by a thin conductor formed on the outer conductor.

The reactance inductive property can be realized by a thin wire electrically attached to the outer conductor.

The reactance inducing property can be electrically connected to the capacitive ring.

The capacitive ring may be adjacent to, close to, or in position of the feed point of the radiating element.

The radiating element may be separated from the reactance characteristics, but is designed to work with it.

The reactance characteristics can exhibit high impedance to the surface current on the coaxial feed by offsetting the antenna mismatch.

Also provided are devices or methods substantially described herein with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied to other aspects of the invention in any suitable combination. For example, the characteristics of the device may be applied to the characteristics of the method and vice versa.

Next, an embodiment of the present invention will be described as a non-limiting example, and will be shown in the following figure.

It is a schematic equivalent circuit showing the characteristics of the matching choke according to one embodiment. FIG. 3 is a diagram of a monopole antenna including a double conductor matching choke according to an embodiment. It is a figure which shows the plurality of conductor configurations by a plurality of embodiments. It is a longitudinal sectional view of the modification of the monopole antenna including the double conductor matching choke according to one Embodiment. It is a figure of the modification of the monopole antenna including the single conductor matching choke by one Embodiment. It is a longitudinal sectional view of the modification of the monopole antenna including the single conductor matching choke according to one Embodiment. It is sectional drawing in the longitudinal direction of the modification example of the monopole antenna including the three-conductor matching choke according to one Embodiment. It is a figure of the modification of the monopole antenna including the molding / step-like matching choke element by a plurality of embodiments. It is a figure of the modification of the monopole antenna including the inductive / capacitive discontinuity by one Embodiment. It is a figure of the modification of the monopole antenna including a plurality of inductive / capacitive discontinuities by one Embodiment. It is a figure of the modification of the monopole antenna including a plurality of step-like inductive / capacitive discontinuities by a plurality of embodiments. It is a figure of the modification of the monopole antenna which has a matching choke by a plurality of embodiments. It is a simulation plot of the SAR pattern at 2.45 GHz of a monopole antenna without a matching choke element. It is a simulation plot of S11 about a monopole antenna without a matching choke element. It is a simulation plot of the necrosis pattern at 2.45 GHz of a monopole antenna without a matching choke element. 6 is a simulation plot of a SAR pattern at 2.45 GHz for a monopole antenna with a matching choke element. 6 is a simulation plot of S11 for a monopole antenna with a matching choke element. 6 is a simulation plot of a necrosis pattern at 2.45 GHz for a monopole antenna with a matching choke element. A comparison of simulation plots of necrosis patterns at 2.45 GHz for monopole antennas with and without matching choke elements. It is a photograph of a monopole antenna having a matching choke element. It is a macro photograph of an inductive conductor from a matching choke element. A set of photographs of a monopole antenna with a matching choke element constructed using wire conductors. A set of photographs of antenna ablation patterns created by a monopole with a matching choke element. A set of photographs of antenna ablation patterns created by a monopole with a matching choke element. It is a schematic diagram of the system by one Embodiment.

Antenna components that provide impedance matching and reduce or eliminate surface current can be referred to as matching chokes. Matching chokes can provide high impedance discontinuities that perform impedance conversions to match the radiating element to the transmission channel. The matching choke can simultaneously limit the return of surface current to the outer conductor of the transmission line.

The equivalent circuit representing the antenna matching choke is shown in the circuit diagram of FIG.

In the embodiment of FIG. 1, the antenna comprises a coaxial feed, a radiating element, and a matching choke. The antenna may be, for example, an antenna as described later with reference to FIG. In the embodiment of FIG. 2, the monopole radiating element 7 is formed by cutting a part of the outer conductor and the dielectric 8 of the coaxial cable so that the exposed portion of the inner conductor protrudes and acts as the monopole radiating element 7. Formed from coaxial cable. The portion of the coaxial cable that extends to the base of the monopole radiating element 7 functions as a coaxial feed that delivers energy to the monopole radiating element 7.

In this simple circuit, the series inductance of the coaxial feed is represented by the inductor 1. The series capacitance of the coaxial feed is represented by the capacitance 2. The circuit also includes a reactance element in parallel with the coaxial feed line inductance. The reactance element represents the reactance characteristic of the matching choke. The reactance element has a capacitance characteristic 3 and an induction characteristic 4.

In the embodiment shown in FIG. 2, the reactance LC element is realized as a short-circuit slot in the coaxial outer conductor. The short circuit slot function suppresses the surface current and creates a high impedance point in the circuit that matches the antenna impedance (Z antenna) with the coaxial feed line impedance (Z feed line). For example, the coaxial feed line can be 50 ohms or 75 ohms, or any other standard coaxial feed impedance. The antenna impedance can be any impedance, eg, any impedance from 70 ohms to 300 ohms. Antenna impedance depends on the design of the antenna and the tissue for which radiation is intended. Impedance matching may be such as to provide the desired degree of matching, eg, to achieve antenna reflection attenuation between 12 dB and 15 dB.

An example of realizing a matching choke is shown in FIG. FIG. 2 includes three figures of the same antenna. In the first (upper) figure, the components of the antenna are shown in contour. In the second (center) and third (lower) figures, the conductive components are displayed in black to distinguish them from the non-conductive components. The third figure shows that the antenna has rotated about 90 degrees around its longitudinal axis as compared to the first and second figures.

In the embodiment of FIG. 2, the matching choke is applied to a simple monopole antenna. In other embodiments, the matching choke may be applied to any other antenna type, not limited to monopoles.

The radiating monopole 7 is separated from the outer conductor of the coaxial feed by the insulating dielectric 8 of the coaxial feed. The radiating monopole 7 is detuned to create a mismatch between the radiating monopole 7 and the coaxial feed used by the matching choke.

The metal conductive portion is represented by a portion 9 (inductive feed), a portion 11 (capacitive ring) and a portion 10 (coaxial outer conductor). The slot 5 in FIG. 2 is a region where the outer conductor of the coaxial feed is removed to expose the inner dielectric 8 and its inductive characteristics are changed. In this embodiment, at least a portion of the inner dielectric 8 remains in place when the region of the outer conductor is removed. In a further embodiment, the region of the inner dielectric 8 is also removed, exposing a portion of the inner conductor. The exposure of the inner conductor can be beneficial when the high dielectric material is placed in close proximity to the exposed portion. In some situations, proximity to the highly dielectric material may be utilized to reduce the size of the slot.

Slot 5 extends longitudinally along a portion of the coaxial feed. The slot 5 extends around the coaxial feed, for example, about 120 to 150 degrees. An additional slot 5A is located on the opposite side of the coaxial feed from slot 5 and has the same ratio as slot 5.

Slots 5 and 5A do not extend to the distal end of the coaxial feed. When a portion of the outer conductor is removed to form slots 5 and 5A, a ring of outer conductor material remains at the distal end of the coaxial feed. This ring may be referred to as the capacitive ring 11.

The parallel inductive element shown in the schematic as the inductive element 4 is generated by the conductor element 9, which may be referred to as an inductive feed. The conductor element 9 joins the main body of the outer conductor of the coaxial cable to the ring element 11 in the vicinity of the monopole feed point. The conductor element 9 is formed from a portion of an outer conductor that remains between slot 5 and slot 5A. An additional conductor element 12 is on the opposite side of the coaxial feed.

Slots 5 and 5A and the corresponding ring elements 11 formed in the outer conductors equilibrate with the inductive elements 9 and 12 to form a capacitive characteristic that aligns the monopole with the coaxial feed line. At the same time, the inductive elements 9 and 12 provide a high impedance path for suppressing the surface current flowing through the outer conductor 10. In this embodiment, two conductive strips 9, 12 are arranged in the radial direction to provide a balanced pair of inductive conductors. Since the inductive conductors 9 and 12 are arranged apart from the radiating element 7, they do not interfere with the roundness of the radiation field on the tangential axis.

A large number of cross sections of the antenna of FIG. 2 are shown in FIG. The first (upper) view of FIG. 3 shows a side view of the antenna. The second (lower left) and fourth (lower right) figures show the axial cross sections of the antenna of FIG. 2, respectively. The third (bottom center) figure shows an axial cross section of a similar antenna in which the material of the outer conductor is removed in different ways to form different profiles of the remaining conductive strips.

In the embodiment of FIG. 2, the conductors 9 and 12 are formed by removing a portion of the outer conductor material, leaving the conductor elements 9 and 12 with reduced widths. This material is placed on the central axis by, for example, sawing, slicing, cutting, burning, melting, erosion, flattening, polishing, hydroforming, machining, laser cutting, or any other method for removing it. It can be removed so that it is perpendicular to it.

Further, in the example shown in the third figure of FIG. 3, the material may be removed so as to have an arbitrary angle 13 at the edges of the conductors 9A and 12A. Angle 13 may represent an undercut from an etching or acid erosion process. In a further embodiment, the coaxial cable can be manufactured with the gaps 5 and 5A already in place.

FIG. 4 shows two additional cross sections of the antenna of FIG. FIG. 4 shows that, for clarity, the conductive coaxial structure in this example is present on only one axis and is discontinuous on the other orthogonal axis. The first (upper) cross section shows a cross section through slots 5 and 5A, indicating the presence of the ring 11 and the remaining outer conductor 10. The second (lower) cross section is taken through the conductive strips 9 and 12, and the outer conductors are visible continuously along the length of the coaxial feed in this cross section.

A further embodiment with a single conductive strip 17 is shown in FIG. FIG. 5 includes four figures. From top to bottom, these are the first direction of the antenna shown in the contour, the second direction of rotation of the antenna shown in the contour, the direction of rotation in which the conductive material is shown in black, and the conductivity. The material contains the first direction shown in black.

In the embodiment of FIG. 5, a single slot 14 is formed on the outer conductor. The single slot 14 may extend around the coaxial feed, for example, from 280 degrees to 310 degrees. A slot length of 302.7 degrees gives a conductor width equal to the radius of the cable. This configuration can also be used to simplify the structure. In some situations, the roundness of the radiation pattern can be minimally affected by imbalance due to the lack of symmetry in the structure of the antenna of FIG. 5, as shown in FIG. FIG. 6 contains four figures, described below from top to bottom. The first (upper) view of FIG. 6 is an axial cross-sectional view of the antenna of FIG. 5, showing a single conductive strip 17. The second figure of FIG. 6 is a side view of the antenna of FIG. The third and fourth (lower) views of FIG. 7 are longitudinal cross sections taken at vertical angles.

Another variant is shown in FIG. 7 with a three-conductor configuration that can provide improved triaxial symmetry or balance the mechanical force between the outer conductor and the capacitive ring 11. .. Three conductive strips 18 are arranged around the coaxial cable. The three conductive strips 18 are arranged between the three slots 19. The first (upper) view of FIG. 7 shows a side view of the antenna of FIG. The second (lower) view of FIG. 7 shows an axial cross section.

Also, as shown in FIG. 8, the arrangement of the inductive conductors may include stepped portions for adding additional capacitance. FIG. 8 contains four figures, described below from top to bottom. The first (upper) figure and the second figure show the embodiment of the first stepped slot in contour (first figure) and with a conductive material represented in black (second figure). show. In the first stepped slot embodiment, the slot comprises a wide portion 21 at the center of the slot and narrow portions 22 and 20 at the ends of the slot. The remaining conductive material is shown as portion 23.

The third and fourth (lower) views of FIG. 8 show an embodiment of the second stepped slot in contour (third figure) and in black, a conductive material (fourth). Figure). The slot in FIG. 8 is narrow at the center 24 and wide at the sides 24A, 24B. In other embodiments, the slots may be widened or narrowed on only one side. Any number or sequence of steps may be used. In some embodiments, the stepped slot can add additional capacitance to this arrangement and / or increase the matching bandwidth between the antenna and the feed line.

Another embodiment includes an inductive element having a capacitive discontinuity 25 as shown in FIG. 9 in a schematic (upper side) and having a conductive material shown in black (lower side). The capacitive discontinuity 25 is formed by making a cut in the conductive strip between the slots. In the embodiment of FIG. 9, the cut 25 is at the proximal end of the conductive strip. In this case, the breaks in the lead wire can further enhance the capacitive characteristics of this arrangement.

Capacitive discontinuities can also be present in many other regions. FIG. 10 shows two additional embodiments with capacitive discontinuities. In the first embodiment of FIG. 9 (shown above), the capacitive discontinuity 26 is at the center of the strip. Multiple discontinuities 27 may be created to filter or tune bandwidth performance. The second embodiment shown in FIG. 10 (bottom) shows two capacitive discontinuities 27 in a single capacitive strip. In other embodiments, capacitive discontinuities of any suitable number or location may be used.

The discontinuities may be further spaced in any stepped arrangement 28 of various lengths or spaces. An embodiment having a stepped arrangement of discontinuities is shown in FIG. 11, and a stepped arrangement of discontinuities 28 is shown in the inset. The embodiment of FIG. 11 has a plurality of stepped inductive / capacitive discontinuities, which are offset from each other both in the longitudinal direction and around the antenna.

FIG. 12 shows various combinations of monopole antennas that can be used with matching chokes, for example to minimize size. The first embodiment shown in FIG. 12 (left figure) includes a helical radiating element 30. The second embodiment shown in FIG. 12 (center view) comprises a plurality of slots 29 offset in the longitudinal direction. The third embodiment shown in FIG. 12 (right figure) includes a dielectric coating 31 covering a portion of the inner conductor forming the radiating element. Other antenna types can be used and operated with the same technique. Any suitable combination of antenna type and reactance element may be used.

A large number of slots can be used to further enhance surface current attenuation. An example of a typical monopole radiation pattern is shown in FIG. In the example of FIG. 13, the monopole has a simple coaxial structure without a matching choke element. In the computational plot of FIG. 13, Specific Absorption Rate (SAR) represents a measure of the rate at which energy is absorbed by the tissue. This plot shows the SAR of the region around the monopole radiating element 100. Region 102 of the highest SAR has a teardrop shape extending posteriorly along the radiating element.

This plot was made for a spot frequency of 2.45 GHz. In this particular example, the monopole is inconsistent at the frequency of interest (2.45 GHz), as described in the simulated S11 reflection attenuation plot of FIG. Line 104 represents the amount of reflection attenuation of the antenna whose SAR plot is shown in FIG. The lowest point 106 of this line is a frequency lower than the desired spot frequency. A simulated necrosis pattern for the antennas of FIGS. 13 and 14 is shown in FIG. The necrotic region 108 has a teardrop shape extending posteriorly along the radiating element.

The radiation pattern for the modified version of the monopole of FIG. 13 is shown in FIG. The monopole 110 has the same simple structure as shown in FIG. 13, but has a matching choke element. The plot of FIG. 13 was made for the same spot frequency of 2.45 GHz. In this calculated plot, the Specific Absorption Rate (SAR) pattern 112 is truncated on the vertical axis to indicate attenuation of the surface current on the surface of the antenna feed line. The second figure shows that the SAR pattern is substantially symmetric about the longitudinal axis of the antenna.

In this particular example, the mismatched monopole is centered on operation at the frequency of interest (2.45 GHz), as shown in the simulated S11 reflection attenuation plot of FIG. 17, where line 114 represents antenna reflection attenuation. Has improved matching over a wide bandwidth. The desired frequency is indicated by the marker 116.

The simulated necrosis 118 pattern for the antennas of FIGS. 16 and 17 is shown in FIG. It can be seen that the pattern 118 has a more spherical shape as compared with the design without the matching choke. A side-by-side comparison of necrotic patterns for antennas with a simple antenna 108 and a matching choke 118 is shown in FIG. The ideal spherical zone is indicated by the dashed circle 120. It can be seen that the pattern with the matching choke is closer to the desired spherical pattern.

The shape of the necrotic region can be further optimized by using multiple inductive conductor / slot pairs to add further surface current reduction. The overall design is balanced when all these factors interact with respect to antenna mismatch, overall S11 alignment, and radiation pattern.

FIG. 20 shows an example of a monopole antenna configured by using a matching choke element. In this example, a 4 mm x 0.8 mm slot 32 is laser-removed from a 1.19 mm diameter coaxial cable (Sucoform 47) and is joined to a 0.5 mm wide capacitive ring 33 with a width of 0.65 mm x length. Two 4 mm conductive interconnects are left. The outer conductor is completely removed to expose the inner conductor so as to form the radiating monopole 34. In a more detailed picture of FIG. 21, the outer conductor 35 is laser ablated to expose the dielectric 36 and leave the conductive bridge 37.

In another arrangement shown in FIG. 22, a Sucoform 47 cable is constructed with two 3 mm × 1 mm slots and a 1.5 mm capacitive ring to feed a 19 mm sealed monopole.

In this embodiment, instead of leaving a conductive strip of outer conductor material between the slots, different forms of conductive interconnects were used. The conductive interconnects were two 0.45 mm (25 AWG) wires attached to electrically bridge the gaps forming the slots. This configuration was considered as an alternative (cost-effective) manufacturing method to verify whether the same performance could be achieved by other means.

The manufactured antennas were tested in in vitro bovine liver (10 ° C storage) to determine radiation patterns. FIG. 23 shows the radiation zone in the in vitro tissue for 70 W of irradiated 2.45 GHz microwave energy. In this photo, a substantially circular 3 cm (1.18 inch) ablation zone can be seen. An additional line from the center to the outside (2 o'clock line in FIG. 23) is made by a hole for placing the fiber optic temperature probe (T1S-02-WNO) used to measure the ablation zone temperature. rice field. Higher power 100 W ablation is performed on the same antenna and is shown in FIG.

It has been found that the methods described above can produce more desired ablation patterns with limited surface currents, utilizing minimal materials to construct highly efficient and cost effective radiators.

FIG. 25 shows a microwave system generally indicated by 110 for treating tissue. The microwave system 110 includes a microwave generator 111 for supplying microwave energy, a flexible interconnect microwave cable such as a coaxial cable 112, a handgrip or handpiece 113, and a microwave antenna device 114. The microwave generator 111 includes a controller 115 configured to select the frequency of the microwave energy provided to the cable device and / or the power of the microwave energy provided to the cable device.

In a plurality of embodiments, a reactance element (not shown in FIG. 25) is formed on or in the microwave cable 112. The reactance element is configured to match the impedances of the cable 112 and the antenna device 114. The reactance device may include any of the reactance devices described above in connection with FIGS. 1-12. The reactance element may be tuned to operate in a selected operating frequency or frequency range.

The microwave cable 112, reactance element, and antenna device 114 may be similar to any cable, reactance element, and antenna device described above with reference to any of FIGS. 1-12.

In use, the controller 115 selects an operating frequency or frequency range and controls the microwave generator 111 to supply microwave energy in the operating frequency or frequency range to the microwave cable 112.

The antenna device 114 is placed in or adjacent to tissue, such as the tissue of a human patient or other subject. The antenna device 114 radiates microwave energy to the tissue to heat the tissue. Tissue heating may be such that it causes ablation.

During operation, the reactance element at least partially matches the impedance of the antenna device 114 with the impedance of the microwave cable 112. The reactance element also reduces or eliminates the surface current on the microwave cable 112. The reactance device parameters are selected to equilibrate the matching with respect to the reduction in surface current. In multiple embodiments, the design process is used to design a reactance element, which can be called a matching choke. Radiating elements (eg, monopole antennas), microwave feed lines (eg, coaxial cables), and matching chokes are simulated using any suitable simulation software. The parameters of the radiating element and the matching choke are adjusted until the matching choke substantially matches the microwave antenna to the microwave feed line and at the same time reduces or eliminates the surface current on the microwave feed line. In some embodiments, an iterative design process is used in which the radiating element is detuned to obtain a mismatch between the radiating element and the microwave feed line at the desired operating frequency. The matching choke parameters are adjusted to compensate for the inconsistency. Detuning and parameter adjustment may be repeated until the value of the parameter that reduces or eliminates the surface current on the microwave feed line is obtained while substantially matching the microwave antenna to the microwave feed line. Matching choke parameters include, for example, slot width, slot length, slot position, number of slots, ring width, ring position, number of rings, conductive strip length, conductive strip width, conductive strip position, wire length, It may include wire width, wire position. Matching choke parameters may include the inductance value of at least one inductor. Matching choke parameters may include the capacitance value of at least one capacitor.

In some situations, the alignment may change depending on the type of organization. For example, tissues with low water content, such as lungs, may not match as well as tissues with high water content, eg liver. Consistency can be improved or reduced depending on how the changing dielectric affects the overall design. Therefore, different designs can be used for different target dielectrics. In the design, a dielectric constant 43 can be used for the liver at 2.45 GHz. A dielectric constant of 20.5 can be used for lungs inflated at 2.45 GHz. A dielectric constant of 48.4 can be used for lungs contracted at 2.45 GHz.

Different designs can be used for different cable diameters.

In some situations, the slots are shorted and the amount of slots can be doubled to improve attenuation. Adding more slots may add more filtering elements. For example, two sets of two slots may be used.

In the design, high priority may be given to attenuating surface waves to improve the sphericity of the pattern.

The length of the monopole, for example, determines a possible mismatch between 10 dB and 12 dB at the frequency of interest. In an exemplary design, increasing the slot length increases the inductance. The slot conductor element 9 increases its capacitance as it expands.

As the thickness of the conductor element decreases, the inductance increases. The overall length of the slot may be shortened to produce a compensatory effect that increases capacitance as the top of the slot approaches the bottom of the slot.

The height of the ring element 11 increases or decreases the capacitance. The higher the height, the larger the capacitance, and the lower the height, the smaller the capacitance.

In practice, the design process can start with a monopole. Ring elements 11 and slots are then introduced to optimize length and width for a given cable diameter and tissue type. Ring element and slot parameters are optimized to improve matching and ablation zone geometry at the same time.

The goal for matching may be to achieve a reflection attenuation of 12 dB to 15 dB at the frequency of interest. Designs such as those described above have been found to provide very wide bandwidth frequency matching. It has been found that further improvements in alignment can sacrifice the ablation shape and vice versa.

In the above embodiment, the monopole antenna is formed from a coaxial cable. The monopole antenna includes an exposed portion of the inner conductor of the coaxial cable. In other embodiments, the antenna may be formed from coaxial cable or coupled to coaxial cable in any suitable manner.

The above embodiments are described with respect to coaxial cable, but in other embodiments any suitable transmission line may be used. Any suitable reactance element may be formed in or on the transmission line.

It will be appreciated that the invention is purely described above as an example and that detailed modifications can be made within the scope of the invention. Each feature disclosed herein, as well as claims and drawings (where appropriate), may be provided independently or in any suitable combination.

Claims (23)

With a microwave feed line configured to deliver microwave energy with a selected operating frequency or frequency range to a radiating element extending from or coupled to the distal end of the microwave feed line. ,
With the radiant element
The reactance element formed in or on the microwave feed line is provided.
The operating frequency or frequency range is such that the reactance element provides a desired degree of matching between the impedance of the radiating element and the impedance of the microwave feed line and the surface current flowing to the ground of the feed line. A microwave device selected to reduce or eliminate. The microwave device according to claim 1, wherein the microwave feed line includes a coaxial cable, and the grounding includes an outer conductor of the coaxial cable. The microwave device according to claim 2, wherein the reactance element includes at least one opening formed in the outer conductor by selectively removing a part of the outer conductor of the coaxial cable. The microwave device of claim 3, wherein the at least one opening comprises at least one longitudinal slot. The microwave device according to claim 4, wherein at least one conductive strip remains between the longitudinal slots, and the at least one conductive strip forms an inductive conductor element. The microwave device according to claim 5, wherein the reactance element further includes at least one conductive wire arranged across the at least one longitudinal slot, thereby forming an inductive conductor element. The reactance element includes at least one capacitive ring at the distal end of the coaxial cable, and the capacitive ring or each capacitive ring comprises a ring of outer conductor material that remains after the formation of the at least one opening. , The microwave apparatus according to any one of claims 4 to 6. The microwave device according to claim 5, wherein the at least one capacitive ring is electrically connected to the at least one inductive conductor element. 5. The invention of claim 5 or 6, wherein the inductive conductor element comprises at least one discontinuity along the length of the inductive conductor element, wherein the at least one discontinuity provides capacitance. , Or the microwave apparatus according to claim 7 or 8, which is subordinate to claim 5 or 6. The microwave device according to any one of claims 4 to 9, wherein the at least one longitudinal slot varies in width along the length of the slot. The microwave device according to any one of claims 4 to 9, wherein the at least one longitudinal slot has a stepped width such that different portions of the longitudinal slot have different widths. The microwave device according to any one of claims 4 to 11, wherein the at least one longitudinal slot is a single longitudinal slot. The microwave device according to any one of claims 4 to 11, wherein the at least one longitudinal slot is a pair of radially opposed longitudinal slots. The microwave device according to any one of claims 1 to 13, wherein the radiating element includes a monopole antenna. The radiating element comprises the exposed distal portion of the inner conductor of the coaxial cable, wherein the inner conductor of the coaxial cable is longer than the outer conductor of the coaxial cable, according to claim 2 or claim 2. The microwave device according to any one of claims 3 to 14, which is subordinate to the above. The microwave device according to any one of claims 1 to 15, wherein the surface current includes a common mode current. The microwave device according to any one of claims 1 to 16, wherein the microwave device is configured to perform microwave ablation and / or tissue hyperthermia of a tissue in the operating frequency or frequency range. With a microwave generator,
A controller configured to control the microwave generator to generate microwave energy with a selected operating frequency or frequency range.
A microwave feed wire configured to deliver said microwave energy to a radiating element extending from or coupled to the distal end of the microwave feed wire.
With the radiant element
The reactance element formed in or on the microwave feed line is provided.
The operating frequency or frequency range is such that the reactance element provides a desired degree of matching between the impedance of the radiating element and the impedance of the microwave feed line and the surface current flowing to the ground of the feed line. A microwave system selected to reduce or eliminate. A step of controlling the microwave generator to generate microwave energy with a selected operating frequency or frequency range,
A step of delivering the microwave energy by the microwave feed line to a radiating element extending from or coupled to the distal end of the microwave feed line, in or on the microwave feed line. Including the step of forming the reactorance element in
The operating frequency or frequency range is such that the reactance element provides a desired degree of matching between the impedance of the radiating element and the impedance of the microwave feed line and the surface current flowing to the ground of the feed line. A method selected to reduce or eliminate. How to design a microwave device
A step of simulating operation at a selected frequency or frequency range of a radiating element extending from or coupled to the distal end of a microwave feed line.
A step to perform an iterative design procedure
The steps include simulating the detuning of the radiating element and selecting the reactance characteristics of the reactance element formed in or on the microwave feed line.
At the selected frequency or frequency range, the reactance characteristics of the reactance element provide the desired degree of matching between the simulated impedance of the radiating element and the simulated impedance of the microwave feed line. A method in which the iterative design procedure is repeated until the simulated surface current flowing through the ground of the feed line is reduced or eliminated. With the steps to provide coaxial cable,
A step of selectively removing the distal portion of the outer conductor of the coaxial cable to expose the distal portion of the inner conductor so as to form a radiating antenna element at the distal end of the coaxial cable.
Including the step of forming at least one opening in the outer conductor of the coaxial cable by selectively removing at least one additional portion of the outer conductor of the coaxial cable.
The parameters of the at least one opening provide the desired degree of matching between the impedance of the radiating element and the impedance of the microwave feed line when operated in a selected operating frequency or frequency range. , A method of manufacturing a microwave device selected to reduce or eliminate surface current flowing through the ground of the feed line. 21. The method of claim 21, wherein the at least one opening comprises at least one longitudinal slot. Selective removal of the at least one additional portion of the outer conductor is sawing, slicing, cutting, burning, melting, erosion, flattening, polishing, hydroforming, machining, laser cutting, etching, acid erosion. The method of claim 22 or 23, comprising at least one of.

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